Design And Principle Of Protection Device Of Power Capacitor

As a typical passive components, capacitor is an important reactive power compensation equipment, and is widely used in power systems. Traditional protection relaying have disadvantages and limitations, leading to many kinds of defaults occur. Now integrated devices are developing, which contain many functions, such as protection, measurement, control, communications and so on. Theses devices are powerful to resole the problem of capacitor’s protection and effective run. This paper summarizes the evolvement and actuality of capacitor protection, basing on which an idea is raised for developing a series of new protection devices integrated with measurement, control, to satisfy occasion’s requirement of power plant and110kV substation. And the develop or the devices and the key technologies are discussed.First, the paper described the principle of protection of the capacitor protection devices, the main design principles and functional requirements. Basing on this, the paper proposed corresponding protection function of different fault. For example, when a short circuit emerge on the connection between the capacitor and the circuit breaker to take instantaneous or short delay over current protection; when the capacitors find internal fault, or capacitor leads produces short circuit, to install the transverse differential protection; When the capacitor encounters low-voltage or over voltage to install low/over voltage-protection; When the single-phase ground to take protection of zero sequence current.Then, the paper introduces the hardware design and software design of the device. Super performance, general-purpose, economical, anti-jamming, expansibility and other factors are considered for hardware design. The system uses DSP and ARM as the system control processing unit. Around the dual-processor unit, the paper details the various modules of the hardware, such as data acquisition/conversion module, switch in/switch out module, communication module, and power module. We select CPLD to deal with the data transferring between the DSP and ARM, The application of CPLD greatly simplifies the hardware design. The software is organized by programming modules to simplify software design and improve expansibility. The writing of every functions of software are independent, and finally the joint debugging. As for computer relaying algorithms, considering characteristics of capacitors, Full-wave Fourier algorithm combined with different filter algorithm is used. This algorithm eliminates the influence caused by decaying DC.